Lighting baseball fields requires both illuminating the playing surface of the field and providing “uplighting” (i.e., light to the aerial space above and/or proximate the field). Field illumination is typically provided in accordance with at least a minimum accepted standard, such as is found in RP-6-15 of the Illuminating Engineering Society (IES). U.S. Pat. No. 7,976,198 incorporated by reference herein in its entirety discusses the necessity of consideration of aerial lighting levels and provides some examples of measurements of aerial lighting intensity.
It is also known in the lighting industry that lighting that is otherwise satisfactory and meets illumination standards for field lighting can still pose problems when considering uplighting. As discussed in U.S. Pat. No. 7,976,198, light sources can cause glare and reduce playability for some of the players due to the mounting locations and aiming angles of the light sources. For example, a luminaire that provides uplighting but causes reflection on surfaces near the luminaire or internal glow from the luminaire can cause unwanted glare in the eyes of the batter or other players. This glare can obscure the ball and reduce the player's ability to visually track it. U.S. Pat. Nos. 7,976,198 and 9,402,292, also incorporated by reference herein in its entirety, both provide a discussion of some of the considerations that go into determining when uplight is needed, when glare may be perceived, how to adequately design a lighting system to provide uplight while mitigating glare, and the like.
Still further, it is well known in the art of lighting design that improving lighting and reducing cost are primary drivers and can lead to many excellent designs optimized for a specific primary function, but sometimes to the detriment of a secondary function. For example, older designs with less control tended to provide adequate lighting of an aerial space (albeit typically with less control over perceived glare) because visors, etc. were not as precise—particularly for HID lighting. Contrarily, newer designs such as newer LED luminaires exhibit enhanced beam control and while well suited for target areas, no longer have sufficient uncontrolled light that could be used for aerial lighting. This is in addition to the fact that there are still significant areas (older or newer technology) which are lacking in adequate progress. For example, there has been little progress in reducing the number of pole or light mounting locations for wide area lighting applications—progress which could lead to reduced cost.
Consider more specifically beam control and uplight. It is ordinarily considered desirable in the art to control such things as symmetry of the beam, distribution of light within the beam, beam angle, field angle, and cutoff angle, as well as the sharpness of transition from “full” light to “zero” light (or no perceivable light). In the current state of LED design luminaires providing such a transition over an angle of 10 or more degrees are considered to have fairly sharp cutoff (if such is even possible). These luminaires (often referred to as field lighting or downlighting fixtures) are designed such that beam size and intensity closely match the requirements of the target area (which, as stated in the aforementioned patents, is different than needs for uplighting). To achieve these ends, a lighting designer typically relies upon a number of light directing devices such as e.g., secondary lenses, structural components such as adjustable armatures, color gels, filters, and/or lighting redirecting devices (e.g., reflective visors, baffles, light absorbing visors, strips, or rails). Traditionally, uplight could be provided from one or more of these field lighting fixtures from a high mounted position and aimed generally downward, and/or uplight could be provided from one or more of these field lighting fixtures from a low- or mid-mounted position and aimed generally upward. With respect to the former, these luminaires generally have multiple rows of LEDs stacked vertically (i.e., more or less on a plane that is perpendicular to the aiming axis of the luminaire) in several rows so to produce an array. This provides good illumination for field lighting and allows for smooth blending of the light on a playing field from multiple luminaires because of the wide spread and diffuse beam from the elevated position. If an upper visor is used, it provides cutoff that still works well with a somewhat gradual transition of light from full light to full cutoff (ordinarily having a stark cutoff at the top of the beam could even result in undesirable effects on the target area by creating a sharp transition effect on the target area or field where a more gradual transition is typically appropriate). The problem is that it produces too much light for uplighting, in addition to posing potential glare issues because the large array of LEDs are often directly viewable along common lines-of-sight. This is in addition to the fact that the top of a pole is already crowded with field lighting fixtures which are needed for lighting uniformity and blending, and so there is not always space at the top of a pole for uplight fixtures.
That being said, this style of luminaire is also unsuitable for uplighting from a low- or mid-mounted position, as the multiple rows of LEDs create problems by making it very difficult to create a sharp cutoff of light near the edge of the composite beam. FIGS. 5A-B illustrate the problem with using field lighting LED luminaires having multiple rows of LEDs. There is a different angle for cutoff for each row of LEDs due to stacking rows of LEDs in a luminaire housing; in essence, creating multiple focal points which impair the ability to provide sharp cutoff from a single visor or other light redirecting device. This is at least part of the reason why haziness appears when using current LED luminaires as low-mounted uplights—the lack of a distinct cutoff leads to a gradual change in light level that has been described by viewers as “hazy.” These luminaires also tend to exhibit “back light” (light which projects backwards and strikes the pole thereby producing perceived glare).
Yet until now the industry has struggled with how to improve on uplighting techniques. In order for players to see the ball well enough for play several factors need to be considered. First, low-mounted uplights must be aimed so that they have complete cutoff below a horizontal plane through the luminaire lest they cause perceived glare for players. However, for a state-of-the-art luminaire a visor creating a sufficient cutoff for uplighting, and more specifically baseball uplighting, would require a visor on the order of at least three to four times as long as currently in use, which would be prohibitively large for lighting fixtures that need to be as compact as possible (e.g., due to pole loading or EPA needs). Second, ball visibility is closely related to its contrast with its visual background. If the ball is close to the ground, the visual background is fairly bright, and therefore the ball requires a fairly high level of illumination. If the ball is high in a dark sky, a relatively small amount of illumination will allow it to be visible against the dark background. But field lighting luminaires low- or mid-mounted and aimed for uplighting tend to provide very high levels of lighting at the highest part of the aerial zone of play, with diminishing light levels in the lower aerial zone of play—which is the opposite of what is needed. Further, luminaires using LEDs for sports lighting are being packed with more LEDs to provide more lumens per luminaire in order to reduce the number of luminaires on a pole or structure and potentially reduce construction costs by e.g., lowering weight and wind loading of the support structure, and practices such as these which are good for the primary needs of sports lighting can have undesired outcomes for other lighting needs at the same venue (here, uplighting). So, progress in lighting design and specifically field lighting highlights the need for more attention to be paid to the aerial space above and/or proximate the field.
It is further well known that lighting systems for large or wide area applications can have a high cost, and that a major component of the cost is related to the pole or other elevating structure. Poles can be on the order of dozens of feet to over 100 feet tall making them very costly; therefore, it is generally desirable to minimize the number of poles for a given target area. But it can be problematic trying to reduce pole count since certain pole positions which might be desirable which use luminaires according to prior art tend to create glare for certain players. Also, luminaires according to prior art tend to project light into the sky much higher than is needed, which can create a sky pollution issue—regardless of pole count.
FIG. 3C, for example, illustrates a pole configuration that might be desirable. It may be appreciated by a person of skill in the art that if the configuration shown in FIG. 3C were used with light sources according to prior art, there would be significant problems with meeting the exacting requirements of sports lighting (e.g., uniformity, minimum light level, etc.) while also minimizing glare and haze, particularly since the proposed “E” pole location shown is in center field in direct view of a batter. In fact, even in standard 8- and 6-pole configurations with poles in the outfield area walls, blackened boards, or other blocking devices (reference no. 313, FIG. 6A) must be used to prevent back light from distracting a batter. When target area lighting and uplighting are provided from the same or similar design of luminaire, such as when fixture 310, FIG. 6A, which is designed to provide target area lighting from an elevated position on e.g., pole 312 at crossarm 314, is also used as luminaire 311 to provide low-mounted uplighting, this issue is worsened. Furthermore, haze caused by the low-mounted luminaire could impede a player's vision. Haze often occurs during fog, rain, or other atmospheric conditions when particulates cause a scattering or absorption of light, and can be particularly distracting when a luminaire has a beam with a gradual transition from full to zero perceived light. And since the transition from full light to no light in these luminaires occurs over a range of approximately 10 degrees, a mid-pole mounting position in combination with a necessary cutoff of light at horizontal is precluded, since the full light necessary for viewing the ball in the air would not be present at 40 feet in height. It should be noted that often LED luminaires according to prior art when used for baseball uplighting must be mounted low, at some height 320 FIG. 6A (which is on the order of 25 feet) in order to ensure that full light hits at roughly 40 feet elevation from the field. If this low mounting height is not used, adequate modeling of a ball in flight may not be possible.
Shown another way, FIG. 5A illustrates in simplified form the light projected on a wall 650 from an LED luminaire 22 according to prior art; namely, having multiple rows of LEDs. FIG. 5B illustrates a virtual side view of the same luminaire having LEDs 694-697 spaced one inch apart, with representative center beams 684-687, and representative lower cutoffs 674-677. It may be appreciated that center beams 684-687 remain parallel to any distance of projection—with the result that the centers of the beams (also referred to as the central aiming axis of the LEDs) from each LED would be indistinguishable at any distance. But it may be further appreciated that due to the differing relationship of LEDs 694-697 to the furthest edge 652 of visor 651, the lower cutoffs 674-677 diverge in a very short distance. In fact, with a visor length on the order of 16 inches, the beams diverge at approximately 5.5 degrees from each other, which at a distance of 16 inches is again only one inch apart, but at 160 feet is a distance of 10 feet. Thus if luminaire 22 as shown is aimed so that light from LED 694 is cut off 25 feet in the air (which is the effective full cutoff point of the luminaire, equivalent to full darkness 657 FIGS. 5A and 5B), full intensity of the beam will not be achieved until a height of 55 feet. This further illustrates the dilemma of trying to use existing LED luminaires for uplighting, since it is desirable to have light with its greatest intensity very near the lower cutoff, and diminish gradually higher in the air (which is the inverse of what is illustrated by zones 653-657 in FIGS. 5A and B).
So while a mid-pole mounting position would be preferable for preventing onsite glare (i.e., glare as perceived by one at the target area), the gradual cutoff of state-of-the-art fixtures necessitates the lower mounting position; this is in addition to the fact that blocking device 313 may need to be just as tall or perhaps even taller 321 than luminaire 311 if internal glow is present or light sources are directly viewable or haze is a concern. Further, a mid-pole mounting position with a luminaire oriented upwardly can trap balls and aerial detritus.
There is still a need for an LED luminaire which creates a beam design having a sharp lower cutoff and not requiring a sharp upper cutoff, but providing less vertical beam spread than common luminaires used for field lighting. In fact, sports lighting needs such sharp cutoff LED luminaires that move away from the current direction in the state of the art in order to provide several benefits. One desired benefit is to provide sharp cutoff to improve playability and to provide precise uplighting to adequately illuminate a ball or other object in flight. It is also generally desirable for uplight to be provided over a precise vertical angle to ensure an object is illuminated over its entire trajectory—without light reflecting back onto the pole (creating a potential glare issue) or light becoming trapped in the luminaire thereby creating an internal glow from the luminaire. It is also generally desirable if uplights avoid excessively long visors or large devices for redirecting light (such as would be currently needed to provide sharp cutoff from arrays of vertically stacked LEDs). Finally, it is generally desirable if uplights in low or mid mounting locations avoid trapping objects falling on them. This can be a problem because even though the lighting fixtures are mounted relatively low, mounting height is still above the reach of a typical person (e.g., to discourage theft or vandalism) which makes the balls or other objects unrecoverable without some kind of lifting mechanism.
What is needed, then, is a different approach to luminaire design which specifically addresses lower light requirements as compared to a target area, low mounting position, sharp lower beam cutoff, reduction or elimination of the issues of back light and haze, reduction or elimination of glare or directly viewable light sources, and addresses the ability to avoid trapping or catching balls, debris, and precipitation.
Thus, there is room for improvement in the art.